Design of asymmetric shape-transition hypersonic inlets

Abstract

P a g e | i AbstractScramjet engines suffer performance penalties at off-design conditions, due to the fact that the engine is designed for one particular set of flight characteristics. Thermal compression has been suggested as one way of addressing poor off-design performance.For thermal compression to occur in the combustor, the incoming airflow must be of a non-uniform pressure distribution. This paper investigates the generation of a non-uniform compression field at the combustor entrance by designing an asymmetric inlet with uneven compression ratios.A complicating factor is that scramjet engines must be carefully body-integrated onto the vehicle forebody to maximise air capture and reduce drag. Any attempt at designing an inlet suitable for thermal compression must body-integrated.One challenge in designing an asymmetric inlet is the current selection of 3D surface modelling tools available to designers. The secondary goal of this project is to improve the current surface generation method for CFD analysis by identifying a new tool to carry out the design process. Ideally, the modelling process should be rapid and user-friendly.The tools selected for this project were 3DReshaper®, Blender™ andMeshLab.This project follows through the design of an asymmetric inlet using a combination of these tools, with a view to providing a non-uniform pressure distribution at the combustor entrance. The ease and usability of the modelling method was evaluated, and found to provide no real improvement over the current method. One tool, Rhinoceros®, has been identified as having potential for future investigation, due to its mesh-to-NURBS surface conversion functionality.The inlet design was tested in an Eilmer4 CFD simulation, and was found to be successful in generating non-uniform pressure distribution at Abstract P a g e | ii the outlet (Figure i). However, an unanticipated shock effect was noted in the inlet, which reduced the effectiveness of the non-uniformity. This effect was due to a shock reflection off the cowl closure point, indicating that a greater understanding of cowl placement is necessary when designing this type of inlet.Figure i -Non-uniform pressure distribution at the inlet exit due to asymmetric inlet shape.Several avenues for future research have been identified. Foremost is an investigation into the cowl closure behaviour contributing to the unwanted shock in the inlet. In addition, testing of new modelling techniques to overcome the problems identified with Blender™ and 3DReshaper® is recommended. Creating a stronger, quicker, easier design process will enable iterative designs to be created and assist in resolving the reflected shock issue. Once this has been completed, a full system analysis can be carried out to determine whether this type of thermal compression inlet has any positive effect on scramjet engine performance.